Deficits in prospective memory following damage to the prefrontal cortex

Neuropsychological investigations of prospective memory (PM), representing memory of future intentions or plans, have evolved over the past two decades. The broadly accepted divisions involved in PM consist of a prospective memory component (PMC), a process for remembering to remember, and a retrospective memory component, a process for remembering the content of the intended action. Previous functional neuroimaing studies have provided some evidence that the rostral prefrontal cortex (BA10) is one of areas that is critical for prospective remembering. However, the question of whether damage to part of the prefrontal cortex affects attenuated performance for PMC remains unresolved. In this study, 74 participants with traumatic brain injury (TBI) including focal damage to frontal or temporal lobe areas were administered thirteen standard neuropsychological tests and the PM task. To identify influential areas contributing to PM performance, discriminant function analysis was conducted. The results indicated that the following three areas are highly contributory to PM performance: the right dorsolateral prefrontal cortex; the right ventromedial prefrontal cortex; and the left dorsomedial prefrontal cortex. Comparing differences in neuropsychological test scores showed that orientation scores were significantly higher in the greater PM performance group, suggesting that PMC represents an integrated memory function associated with awareness of current status. These data contribute to our understanding of the neural substrates and functional characteristics of the PMC.     

Implicit and Explicit Memory in Autism: Is Autism an Amnesic Disorder?

Medial temporal lobe amnesic disorder is characterized by an impairment in explicit memory (e.g., remembering a shopping list) and intact implicit memory (e.g., a woman seems familiar although you cannot remember having met her before). This study examined whether children with high-functioning autism have this same dissociation between explicit and implicit memory abilities. Children with autism and normal development participated in three memory tasks: one implicit task (perceptual identification) and two explicit tasks (recognition and recall). Children with autism showed intact implicit and explicit memory abilities. However, they did not show the typical pattern of recalling more items from both the beginning and end of a list and instead only recalled items from the end of the list. These results do not support the theory that high-functioning autism is a type of medial temporal lobe amnesia. However, these findings suggest that persons with autism use different organizational strategies during encoding or retrieval of items from memory.     

I cannot remember,but I know my past events: remembering and knowing in a patient with amnesic syndrome

Case Y.K. has severe anterograde amnesia and a selective loss of specific personal episodes in his remote memories (Hirano & Noguchi, 1998). In this paper, we attempted to analyze remembering (R) and knowing (K) responses, that is, the relationship between autobiographical remembering and remembering accompanied by subjective experience. Although the rate of R responses was significantly higher than that of K responses in control subjects, Y.K.'s R responses were rare in all subtypes of remote memories. Based on these results, we conclude that Y.K.'s memories on autobiographical incident task were not based on episodic memory but rather on semantic memory. Thus, the autobiographical incidents he could recall were not episodic memory, and his semantic memory made him recall information as fact rather than episode.     

The contribution of familiarity to associative memory in amnesia

In Experiment 1, using the remember/know paradigm with control participants, we compared the contribution of recollection and familiarity to associative recognition for compound stimuli and for unrelated word pairs. It was demonstrated that familiarity makes a greater contribution to associative recognition of compound stimuli than to associative recognition of unrelated word pairs. In Experiment 2, we examined associative recognition memory in medial temporal lobe amnesics, diencephalic amnesics, and control participants for the stimuli employed in Experiment 1. Whereas associative recognition for compounds and unrelated words was nearly identical in control participants, associative recognition was higher for compounds than for unrelated word pairs in amnesic patients. This pattern was observed in the medial temporal amnesic group as well as in the diencephalic amnesic group. These results suggest that associative recognition in amnesia is enhanced to the extent that performance can be supported by study-induced familiarity for the studied pair.     

Prospective memory functioning in people with and without brain injury.

Prospective remembering has been relatively underinvestigated in neurological patients. This paper describes a group study in which the prospective memory performance of 36 people with brain injury and 28 control participants is compared. We used a new instrument, the Cambridge Behaviour Prospective Memory Test (CBPMT) to assess prospective memory. This comprises 4 time-based and 4 event-based tasks. Participants were allowed to take notes to help them remember the tasks. The relationships between CBPMT scores, scores on formal tests and subjective reports on memory, attention and executive functioning were analyzed. The key findings were that (1) note-taking significantly benefited prospective memory performance, (2) significant relationships were found between scores on the prospective memory test and scores on tests of memory and executive functions, and (3) participants had more difficulty with the time-based than with the event-based prospective memory tasks. The results suggest that compensatory strategies improve prospective memory functioning; memory for content as well as attention and executive functioning processes are involved in prospective memory; and that time-based tasks are more difficult than event-based tasks because they place higher demands on inhibitory control mechanisms. Discussion focuses on the implications of these results for neuropsychological assessment and rehabilitation.     

A comparison of egocentric and allocentric spatial memory in medial temporal lobe and Korsakoff amnesics

Two patients with medial temporal lobe damage, seven Korsakoff amnesics and fourteen healthy control subjects were tested on three conditions of a spatial memory test ('short delay', 'allocentric' and 'egocentric'). The task required subjects to recall the position of a single spot of light presented on a board after various delays. The 'short delay' condition tested memory over very short, unfilled intervals. The other two conditions used longer, filled delays. The allocentric condition required subjects to move to a different place around the board before recalling the position of the light. In the egocentric condition stimuli were presented in darkness, which eliminated allocentric cues. The Korsakoff amnesics were impaired at all delays of the short delay tasks, suggesting poor encoding. On the allocentric and egocentric tasks the Korsakoff amnesics showed a comparable impairment in the two conditions, which worsened with delay. This accelerated forgetting suggested that the Korsakoff amnesics also had impaired memory for allocentric and egocentric information. The patients with medial temporal lobe damage were unimpaired in the 'short delay' condition suggesting intact encoding and short-term memory of spatial information. However, they were impaired in the allocentric condition and showed accelerated loss of allocentric spatial information. In the egocentric condition, while the performance of one patient was impaired, the performance of the other was as good as controls. This result suggests that, in contrast to allocentric spatial memory, which is sensitive to medial temporal lobe damage, an intact medial temporal lobe need not be necessary for successful performance on an egocentric spatial memory task.     

Episodic, but not semantic, autobiographical memory is reduced in amnestic mild cognitive impairment

Amnestic mild cognitive impairment (aMCI) is characterized by decline in anterograde memory as measured by the ability to learn and remember new information. We investigated whether retrograde memory for autobiographical information was affected by aMCI. Eighteen control (age 66-84 years) and 17 aMCI (age 66-84 years) participants described a personal event from each of the five periods across the lifespan. These events were transcribed and scored according to procedures that separate episodic (specific happenings) from semantic (general knowledge) elements of autobiographical memory. Although both groups generated protocols of similar length, the composition of autobiographical recall differentiated the groups. The aMCI group protocols were characterized by reduced episodic and increased semantic information relative to the control group. Both groups showed a similar pattern of recall across time periods, with no evidence that the aMCI group had more difficulty recalling recent, rather than remote, life events. These results indicate that episodic and semantic autobiographical memories are differentially affected by the early brain changes associated with aMCI. Reduced autobiographical episodic memories in aMCI may be the result of medial temporal lobe dysfunction, consistent with multiple trace theory, or alternatively, could be related to dysfunction of a wider related network of neocortical structures. In contrast, the preservation of autobiographical semantic memories in aMCI suggests neural systems, such as lateral temporal cortex, that support these memories, may remain relatively intact.     

Performance of schizophrenia patients on time-, event-, and activity-based prospective memory tasks

The present study aimed to determine whether individuals with long-term schizophrenia have impaired prospective memory (PM), the ability to remember to perform intended actions in the future. Three PM tasks (time-, event-, and activity-based) were administered to 60 schizophrenia patients and 60 matched controls. Patients performed significantly more poorly than controls on all three tasks. The between-group difference was disproportionately larger on the time-based task, a task that required a prefrontal lobe process called self-initiated retrieval. To examine the relationship between PM and prefrontal lobe functions, subjects were also administered the Design Fluency Test (DFT), the Tower of London (TOL), and the Wisconsin Card Sorting Test (WCST). For patients, performance on the event-based task was found to correlate significantly with performance on the DFT, and performance on the time-based task was found to correlate significantly with performance on the TOL. Results of this study support the importance and contribution of prefrontal lobe processes in prospective remembering and have implications for the assessment and treatment of individuals with schizophrenia.     

White Matter Integrity and Episodic Memory Performance in Mild Cognitive Impairment: A Diffusion Tensor Imaging Study

White matter (WM) integrity in the medial temporal lobes and episodic memory performance were examined in patients with mild cognitive impairment (MCI) and age-matched cognitively intact controls. Material specific associations between WM in the left versus right hemisphere and verbal versus visual memory performance were examined as well. Fourteen right-handed amnestic MCI patients underwent diffusion tensor imaging (DTI) and received verbal (words, story) and visual (designs) memory tests. Delayed verbal memory was significantly correlated with loss of WM integrity in the medial temporal lobe. This finding was associated with both the left and right temporal regions. Immediate visual memory performance was significantly correlated with the loss of WM integrity in the left temporal region. The results indicate that WM integrity in the medial temporal lobe is associated with objective memory functioning in MCI. However, strong material specific relationships were not observed, possibly reflecting diverse encoding strategies used by participants such as imagery of verbal material and verbal encoding of designs. This research was supported by a pilot grant from the Emory Alzheimer’s Disease Research Center (NIH-NIA 5 P50 AG025688).     

A study of performance of delayed intentions in multiple sclerosis

The ability to remember and perform delayed intentions was investigated in a sample of 40 participants with Multiple Sclerosis (MS) and compared to a group of 36 healthy, neurologically intact, control participants. Using a model of task division, performance on both the prospective memory (PM) component (a failure to remember to do something at a specific time) and the retrospective memory (RM) component (a failure to remember the content of the intention) of two "naturalistic" delayed intention experimental tasks were examined. Significantly poorer performance of the MS group in completing one of the delayed intention tasks successfully appeared to be primarily attributable to retrospective memory deficits rather than prospective memory deficits. This proposition was further supported by group differences on RAVLT measures of retrospective memory. By utilising a paradigm that enables the nature of failure in performing delayed intention tasks to be identified, specific strategies for the clinical management of MS cognitive deficits can be developed.     

A Study of Performance of Delayed Intentions in Multiple Sclerosis

The ability to remember and perform delayed intentions was investigated in a sample of 40 participants with Multiple Sclerosis (MS) and compared to a group of 36 healthy, neurologically intact, control participants. Using a model of task division, performance on both the prospective memory (PM) component (a failure to remember to do something at a specific time) and the retrospective memory (RM) component (a failure to remember the content of the intention) of two “naturalistic” delayed intention experimental tasks were examined. Significantly poorer performance of the MS group in completing one of the delayed intention tasks successfully appeared to be primarily attributable to retrospective memory deficits rather than prospective memory deficits. This proposition was further supported by group differences on RAVLT measures of retrospective memory. By utilising a paradigm that enables the nature of failure in performing delayed intention tasks to be identified, specific strategies for the clinical management of MS cognitive deficits can be developed.     

A case of unusual autobiographical remembering

This report describes AJ, a woman whose remembering dominates her life. Her memory is "nonstop, uncontrollable, and automatic." AJ spends an excessive amount of time recalling her personal past with considerable accuracy and reliability. If given a date, she can tell you what she was doing and what day of the week it fell on. She differs from other cases of superior memory who use practiced mnemonics to remember vast amounts of personally irrelevant information. We propose the name hyperthymestic syndrome, from the Greek word thymesis meaning remembering, and that AJ is the first reported case.     

Memory impairment in humans after bilateral damage to lateral temporal neocortex

The hippocampus and its adjacent medial temporal regions are crucial for episodic memory. However, it is far less obvious whether other temporal regions beyond the medial part are important for memory processing. The memory performance of a group of patients with bilateral lesions over the lateral temporal lobe sparing the hippocampus was assessed and compared with that of patients with relatively spared cortex and patients with bilateral damage to the lateral temporal lobe and the hippocampus. The results demonstrate that bilateral damage to the lateral temporal lobe results in memory impairment across verbal and visual modalities.     

Episodic memory,semantic memory,and amnesia

Episodic memory and semantic memory are two types of declarative memory. There have been two principal views about how this distinction might be reflected in the organization of memory functions in the brain. One view, that episodic memory and semantic memory are both dependent on the integrity of medial temporal lobe and midline diencephalic structures, predicts that amnesic patients with medial temporal lobe/diencephalic damage should be proportionately impaired in both episodic and semantic memory. An alternative view is that the capacity for semantic memory is spared, or partially spared, in amnesia relative to episodic memory ability. This article reviews two kinds of relevant data: 1) case studies where amnesia has occurred early in childhood, before much of an individual's semantic knowledge has been acquired, and 2) experimental studies with amnesic patients of fact and event learning, remembering and knowing, and remote memory. The data provide no compelling support for the view that episodic and semantic memory are affected differently in medial temporal lobe/diencephalic amnesia. However, episodic and semantic memory may be dissociable in those amnesic patients who additionally have severe frontal lobe damage. Hippocampus 1998;8:205–211. Published 1998 Wiley-Liss, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Hippocampal and temporal lobe atrophy and age-related decline in memory

OBJECTIVES: To evaluate the relationship of memory decline that accompanies aging with structural changes in the medial temporal lobe, in healthy middle-aged and older subjects. MATERIAL AND METHODS: A sample of 35 neurologically non-diseased subjects, between 55 and 70 years of age, were examined in a 5-year follow-up study. Neuropsychological investigation included tests of learning, verbal memory, and visual memory. MRI was performed with a superconducting MRI system operating at 1.0 T, using coronal slices of T1-weighted images. Medial temporal lobe atrophy was rated separately in the neocortical, entorhinal and hippocampal regions. RESULTS: We did not find any statistically significant relationship between mild hippocampal or temporal atrophy and memory test performance. Nor did the longitudinal decline in memory show a relationship with temporal lobe atrophy. CONCLUSIONS: The main outcome of our study was that age-related memory decline was not related to mild temporal lobe atrophy in healthy subjects without mild cognitive impairment. There could be other factors influencing memory functions besides age-related structural changes in temporal lobes.     

Functional neuroimaging of sex differences in autobiographical memory recall

Autobiographical memory (AM) is episodic memory for personally experienced events. The brain areas underlying AM retrieval are known to include several prefrontal cortical and medial temporal lobe regions. Sex differences in AM recall have been reported in several behavioral studies, but the functional anatomical correlates underlying such differences remain unclear. This study used fMRI to compare the neural correlates of AM recall between healthy male and female participants (n = 20 per group). AM recall in response to positive, negative, and neutral cue words was compared to a semantic memory task involving the generation of examples from a category using emotionally valenced cues. Behaviorally, females recalled more negative and fewer positive AMs compared with males, while ratings of arousal, vividness, and memory age did not differ significantly between sexes. Males and females also did not differ significantly in their performance on control tasks. Neurophysiologically, females showed increased hemodynamic activity compared to males in the dorsolateral prefrontal cortex (DLPFC), dorsal anterior insula, and precuneus while recalling specific AMs (all valences combined); increased activity in the DLPFC, transverse temporal gyrus, and precuneus while recalling positive AMs; and increased activity in the anterior cingulate cortex, precuneus, amygdala, and temporopolar cortex when recalling negative AMs. When comparing positive to negative AMs directly, males and females differed in their BOLD responses in the hippocampus and DLPFC. We propose that the differential hemodynamic changes may reflect sex‐specific cognitive strategies during recall of AMs irrespective of the phenomenological properties of those memories. Hum Brain Mapp 34:3320–3332, 2013. © 2012 Wiley Periodicals, Inc.     

The contribution of autobiographical significance to semantic memory: evidence from Alzheimer's disease, semantic dementia, and amnesia

In a previous study [Memory Cognit., in press], we demonstrated that some semantic concepts are more likely than others to be associated with specific personal memories, and that this autobiographical significance gives these concepts special status in long-term memory. In this paper, we explore the possible neural correlates of autobiographically significant semantic knowledge and examine whether or not autobiographical significance is a factor in determining patterns of semantic memory loss caused by brain damage. Using famous names that were rated on various attributes, including autobiographical significance, by control participants in a norming study [Memory Cognit., in press], we found that semantic dementia (SD) patients were more likely to recognize, identify and remember autobiographically significant episodes involving famous names that were rated high in autobiographical significance as compared to equally familiar names that were rated low. By contrast, people with Alzheimer's disease (AD) and people with medial temporal lobe (MTL) amnesia did not exhibit this preference for names rated high in autobiographical significance. Furthermore, in tests of free recall, recognition, fame judgment and speeded reading, semantic dementia patients demonstrated a performance advantage for autobiographically significant famous names, whereas the other patient groups did not. These findings suggest a critical role for medial temporal regions in the mediation of autobiographical memory and the interaction between personal experience and semantic memory. Theoretical implications are discussed.     

Perception and recall of faces and facial expressions following temporal lobectomy

The perception of and memory for faces, with or without emotional content, were studied in 43 patients with temporal lobe epilepsy who had undergone unilateral resection of the hippocampus and the amygdala and in 43 healthy participants for comparison. Each participant performed four tasks from the Florida Affect Battery (Facial Discrimination, Affect Discrimination, Affect Naming, Affect Selection) and two memory tasks (in one case of a face and in the other of a facial expression). Findings indicated that, although patients with unilateral temporal lobectomy (right or left) showed no difficulty in discriminating faces, they were not as good at remembering faces. Also, patients who had had a left temporal lobectomy showed impairment in discriminating facial expressions, in the memory of a facial expression and/or in naming facial expressions.     

Looking to the future: automatic regulation of attention between current performance and future plans

We investigated neuro-cognitive mechanisms involved with coordination of attention between current task performance and future action plans in prospective memory. We developed a novel task paradigm with continuous performance of a prospective memory task, where trial intervals of prospective memory targets were systematically manipulated in a periodic cycle of expanding and contracting target intervals. We found that subjects’ behaviour was significantly modulated without awareness of this temporal sequence of the targets: remembering to perform a prospective memory response to target events was more successful and faster in the expanding target interval phase, at the cost of lower and slower performance of ongoing tasks, while an opposite direction of this trade-off effect was observed in the contracting target interval phase. By using functional magnetic resonance imaging (fMRI), we identified the similar trade-off effect in activations in the anterior medial prefrontal cortices (activation elevation at the target responses as well as deactivation at the ongoing responses in the expanding phase as compared with the contracting phase). The opposite direction of the trade-off was observed in the anterior cingulate cortex. These results show a clear case in which attention between current task performance and future action plans in prospective memory tasks is automatically regulated without particular task instructions or strategic control processes initiated by subjects. We suggest that medial areas of the frontal cortex specifically mediate the automatic coordination of attentional resources between current task performance and future action plans.     

Prospective memory in adults with traumatic brain injury: an analysis of perceived reasons for remembering and forgetting

Reasons for prospective remembering and forgetting after traumatic brain injury (TBI) were investigated using Ellis' (1996) five phases of prospective memory as a framework. Participants were 38 individuals with severe TBI and 34 controls. Participants self-rated their perceived reasons for prospective remembering and forgetting using section C of the Comprehensive Assessment of Prospective Memory (CAPM). Significant others also rated participants using the same scale. Analyses were conducted to examine the effect of group membership (TBI or control) on reported reasons for prospective remembering and forgetting. Findings highlighted the TBI group's difficulties with encoding, performance interval, and execution phases of prospective remembering.